Arrays of Ni nanowires were electrodeposited into anodic alumina oxide templates with various pore diameters and porosity. The magnetization behavior of the Ni nanowire arrays was investigated with ferromagnetic resonance techniques and the vibrating sample magnetometer. Both ferromagnetic resonance spectra and hysteresis loops show that there is a strong dipolar interaction between the nanowires. The easy axis of magnetization is mainly a result of a competition of shape anisotropy and dipolar interaction. With increasing array density, the dipolar interactions increase and the easy axis is tuned from parallel to perpendicular to the wire axis.